It is well known to those skilled in the art that the sound a sheet of paper makes as it moves along a paper transport path is a way of diagnosing the condition of the paper. Quiet or uniform sounds can indicate a normal or problem-free passage of the paper along the paper transport path. Loud or non-uniform sounds can indicate a disruption in the passage of the sheet of paper such as a stoppage due to jamming or tearing or other physical damage of the paper. In commonly assigned U.S. Pat. No. 4,463,607 to Hilton et al., entitled “Apparatus for Detecting the Condition of a Sheet,” a paper transport cylinder with a specialized profile is used to enhance the diagnostic qualities of the paper transport noise in order to detect paper wear. The problem with this approach is that the specialized paper transport cylinder is designed to induce stresses into the paper that would interfere with smooth paper transport at high transport speeds. Commonly assigned U.S. Pat. No. 5,393,043 to Nitta, entitled “Image Forming Apparatus with Automatic Paper Supply Mechanism,” describes using optical or mechanical sensors in order to detect the times of the passage of a sheet of paper at various locations along the paper transport path. If the paper does not arrive at a given location at a given amount of time after the start of transport, a paper jam is inferred. The problem with this approach is that optical and mechanical sensors are highly localized in physical detection range, requiring the use of several such sensors situated along the paper transport path. Commonly assigned U.S. Patent Application Publication No. 2012/0235929 to Hongo et al, entitled “Paper Feeding Device, Image Scanning Device, Paper Feeding Method and Computer Readable Medium,” describes placing a microphone near the beginning of a paper feed path in order to detect the sound of a paper jam in progress. The signal from the microphone is processed by counting the number of sound samples above a given threshold within a sampling window of a given width. If the count is sufficiently large, i.e., above a threshold value, a paper jam is signaled. The problem with this approach is the loss of localized information about the paper as it moves along the transport path as provided by the previously discussed prior art methods. An additional problem with this approach is the lack of automatic adjustment of the threshold value due to factors such as a change in paper type or machine wear.
There remains a need for a fast and robust technique to indicate paper jams along a paper transport path that uses a single paper sensor, processes the signals from the paper sensor simply in a way that incorporates the location of the paper along the paper transport path, and automatically adjusts itself in response to changing paper types and machine wear.